Fomula for Percentage Calculation

I have table for Quality , where data validation sources are YES, NO and Blank , I want a formula (Quality %) where if I choose yes for one box , no for other and blank as well. The percentage should be based on all the three parameters (YES, NO and BLANK).

As per the attached template ,I have three Parameters - YES, NO and BLANK. I want to calculate percentage , for example, if first four boxes are NO and rest six boxes are YES, then the Quality percentage should be 60%, and BLANK should not be considered. help